In a known knee joint motion assist device, an upper frame is secured to an upper leg of a user, and a lower frame is secured to a corresponding lower leg of the user. A rotatable support unit fitted with a drive unit positioned on the outer side of the knee of the user pivotally connects the upper frame and the lower frame to each other. A control unit detects a motion of the user via an acceleration sensor for detecting a motion of the user, and the drive unit provides a drive force to the rotatable support unit upon detection of a prescribed motion of the user so that the motion of the user may be assisted by the rotatable support unit. See JP2015-173739A.
According to the conventional knee joint motion assist device, depending on the attitude of the user in initiating a certain motion such as lifting an object from a floor surface, an undue load may be applied to other parts of the body such as the hip joint so that the user cannot fully receive the benefit of the knee joint motion assist device. Also, if the attitude of the user when initiating a certain motion is not proper, the load on the drive unit may be increased so that the power consumption increases, resulting in a shorter battery life.